Because supercritical fluid can continuously change the volume (density) thereof by regulating the temperature and pressure, values of various properties such as dissolution characteristic and the like can be easily controlled, which makes it possible to utilize supercritical fluid as a refrigerant. Additionally, because the viscosity thereof is low but the diffusivity thereof is high, supercritical fluid is expected to be used for washing; or is expected to be used as a refrigerant because the thermal conductivity thereof is high.
Being easy to get and good in handling and the like because of not having explosive nature, inflammability and the like, water, CO2 and the like are generally used as supercritical fluid. Especially, CO2 has characteristics that the critical temperature is 31° C. and the critical pressure is 7.38 Mpa; that the temperature and the pressure are low but manageability is superior, being compared with other materials; that CO2 is a gaseous body at the atmospheric pressure and the ambient temperature; and the like. Therefore, CO2 is made wide use of as an extracting solvent for materials which are easily affected by heat (such as foods, flavoring ingredients and the like) and as a cleaning agent and the like which utilize the drying characteristics and permeability thereof. Additionally, CO2 is generally used by being pressurized up to no less than 7 to 20 MPa in an extracting equipment or a cleaning equipment that employs the supercritical CO2.
Because a pump for carrying CO2 in such an equipment as mentioned hereinabove is used at high pressure, so-called sealless canned motor type of pump is adopted. In some cases, ball bearings are employed as the bearings and used in solution (supercritical CO2). However, when the pump is used for the food sector or semi-conductor sector, wear of the bearings cannot be permitted in order to prevent foreign objects (particles) from occurring inside the pump.
As an example of the pump, a turbo-molecular pump is disclosed in Patent Literature 1. In addition, a canned motor type of pump is disclosed in Patent Literature 2. As for the rest, a semi-conductor manufacturing method and a semi-conductor manufacturing equipment are disclosed in Patent Literature 3, which prevent heavy-metal contamination of extra-pure water being manufactured by an extra-pure water manufacturing system for manufacturing of semi-conductors.
Patent Literature 1: Patent Application Laid Open as H10-274188
Patent Literature 2: Patent Application Laid Open as 2000-9077
Patent Literature 3: Patent Application Laid Open as 2003-124177